The objective of this investigation is to study human chromosome structure with the aid of fluorescent staining techniques. The type of information sought will be chromosomal localization of various classes of DNA sequences by utilizing the acridines as probes of DNA base composition and secondary structure. Information will be sought by fluorescent staining of chromosomes with quinacrine and acridine orange as well as other fluorescent dyes of as yet uncharacterized specificity which will be studied and evaluated as possible in situ probes of chromosomal DNA strucutre. Regions of human chromosomes rich in DNA which contains uninterrupted stretches of adenylate-thymidylate base- pairs will be characterized both by cytological techniques as well as in terms of chemical and physical analysis of DNA.